Sprayers, particularly in Europe, are often equipped with a diaphragm spray pump. The diaphragm pump is self-priming and can load water or chemical solution from an external source even when there is no head present. Self-priming is necessary, for example, when a tank is filled with water from a ditch, canal or other source that is lower than the sprayer pump. However, such self-priming pumps typically have flow rates on the order of 74 gal/min or less. Centrifugal pumps can achieve flow rates of 150-200 gal/min but must have positive head pressure so that the inlet of the pump is flooded. Therefore, use of the higher capacity centrifugal pump presents problems in situations where the source does not provide such a head pressure.